The present invention relates to generating electrical energy in aircraft by recovering kinetic energy and potential energy.
When an airplane gains on altitude and speed, it increases its kinetic energy Ec and its potential energy Ep, which can be calculated respectively from the following formulas:Ec=½mv2 Ep=mgh where m is the mass of the airplane, v is the speed of the airplane, g is acceleration due to gravity (9.81 m/s2) and h is the height of the airplane relative to the ground.
During a stage of climbing, the airplane increases its speed so as to go from a takeoff speed of about 230 kilometers per hour (km/h) to a cruising speed lying in the range approximately 500 km/h to 800 km/h (Mach 0.82 to 0.84), thereby enabling it to accumulate a very large amount of kinetic energy. Concerning potential energy, present airplanes cruise at an altitude of about 12,000 meters (m).
During a stage of descent, because of the kinetic energy and the potential energy that has been accumulated, the pilot needs to control the speed of the airplane so as to avoid exceeding a critical speed or limiting Mach number referred to as the maximum operating limit speed or Mach number (VMO/MMO) beyond which the airplane can suffer major damage.
Nevertheless, and paradoxically, during stages of descent, the pilot is often obliged to increase engine speed in order to have sufficient energy for pressurizing and conditioning cabin air and also for running electrical devices on board. Under such circumstances, the pilot increases engine speed in order to cover demands for electrical and pneumatic energy while deploying air brakes in order to avoid exceeding the maximum operating limit speed or Mach number (VMO/MMO). That solution is not satisfactory since it leads to excessive fuel consumption in the engines even though they are operating at low speed during this stage of flight (descent).
Consequently, there exists a need to have a source of energy in an aircraft that is suitable for supplying electrical energy, and of doing so independently of engine speed. This need is particularly important since proposals are presently being made to replace the hydraulic means used by most functions of an airplane (e.g. extending landing gear, braking, etc.) with means that are entirely electrical, in particular for the purpose of lightening the overall weight of the airplane.
It is also known to fit the wing tips of airplanes with shells that are substantially in the shape of wing tip tanks in order to reduce the negative effects of wing tip turbulence (vortices), which shells serve to limit drag, and consequently to limit wing tip energy losses.